Process for the coking of liquid hydrocarbons



March 15, 1960 A. H. scHuTTE 2,928,785

PRocEss FOR THE COKING oF LIQUID HYQRocARBoNs original Filed May 28, 1948.

/Uuz l 3i Qi'lc" GAS ND GAsoLlNE 637 i 22 75 7,? J0 JA- msm' vAPoR 40 l.

INVENTOR gewi/2g Schaik' STEAM Aun on. We?

:46 Nl-:Y

United States arent)l PROCESS FOR THE COKING OF LIQUID HYDROCARBONS August H. Schutte, Hastings on Hudson, NY., as-

signor to The Lummus Company, New York, NY., a corporation of Delaware Continuation of application Serial No. 29,752, May 28, 19464.66'1`hs application February 19, 1954, Serial No. 411,

6 Claims. (Cl. 208-166) This invention relates to improvements in continuous reactions wherein heavy hydrocarbons in liquid phase are contacted with a continuously flowing gravity packed bed of discrete particles on which a coke coating is formed, the lighter hydrocarbons being removed in vapor form for further processing. It is a continuation of my application Serial No. 29,752, led May 28, 1948, now abandoned, and is an improvement on the invention described in the copending application Serial No. 3,747, led January 22, 1948, now U.S. Patent 2,561,344 of which I am co-inventor.

In the prior methods ofrconverting heavy or residual hydrocarbons to lighter vapors and a deposit of coke, two major problems have arisen. The first of these concerns the application of the hydrocarbon to the contact mass in such a manner that a maximum of charge may be spread with a minimum of interference to ow by agglomeration. It is apparent that if any ofthe charge tends to collect in pools rather than be converted to vapors, agglomeration may result and that portion of the bed stops owing. As the total chargeV is then spread over less than the designed surface, the moving part becomes over-charged and does not dry'out and may also agglomerate. The alternative is to feed substantially less than the design capacity of charge, butv this materially diminishes the efciency of the unit.

The second substantial problem with continuously circulating contact mass systems is the problem of conveying. Where granular particles of discrete size were used, mechanical elevators several hundred feet in height were required to contantly elevate the many tons of catalyst perhour at temperatures in the range of 900 F. or higher. Not only does this require a very expensive installation, but the operating and maintenance costs are substantial.

The conventional conveyor systems used in the iluid .type processes are not applicable `to the problem at hand since they require the use of linely powdered solids of .highly absorptive nature. With a line powder, any liquid existing as a film on the exterior surfaces of the solid particles will be of suicient thickness, relative to the particle diameter to `cause rapid agglomeration and `clogging in the lift leg and in the reactor. These methods ;are therefore suited to conditions where complete vap orization of the feed oil is the primary objective and are Ywholly unsuited for the conveying of liquid film bearing particles which is a basic requirement of any contact cok- :ing system. It is also apparent that in a fluid system, the coke particles produced are of such minute size as to :be vof low value. In the present invention, large particles of 3%: inch size or larger are available for continuous draw oi as product.

The principal object of my invention is to provide an improved method of elevating a contact mass of discrete particles for continuous hydrocarbon conversion operations by utilizing a liquid of controlled boiling point range which produces vapor under the operating condi- ICC being such that sufficient vaporization of the charge takes` place to carry the particles into the reactor without causing excessively heavy oil to vaporize.

A more general object of my invention is to economil cally handle a discrete granular mass of contact materiall in the return path from the lower part of a reheater tQ the upper part of a reactor, wherein' the particles are elevated and wetted by the hydrocarbon feed, the partial vaporization of which may be supplemented by steam and intermediate boiling liquid for the necessary lifting and temperature eiects. Y

A further object of my invention is to provide a novel method of applying liquid to a contact mass while in thev restricted return path from the reheater to the reactor.

A still further object Yof my invention is to feed a gravity packed, unagitated reaction bed with solids particles carrying heavy oil liquid and continuously moving the particles by gravity progressively and uniformlythrough a reactor from top to bottom so as to obtain an appreciable residence time so that the particles leaving the bed are completely dry. The use of a maximum density, gravity packed, bed not only greatly reduces the required reactor size for a given residence time over thatrequired for a turbulent uidized bed but the absence of turbulence allows a progressive drying out of the particles and prevents any freshly wetted particles from leaving the reaction zone. It will thus be clear that a uidized bed would be entirely unsatisfactory for the present operation--even if large particle sizes were used.

Further objects and advantages of my invention will appear from the following description of a preferred form of embodiment thereof taken in connection with the attached drawing illustrative thereof and in which:

Fig. l is a schematic outline of the principal elements of a contact coking unit. l

Fig. 2 is a detailed cross section of the lower end of the solids transfer conduit.

ln accordance with the preferred form of embodiment of my invention, the reactor 10 for contact coking is mounted at an elevated position so that the contact material flowing therethrough and out outlet 12 will pass by gravity through conduit 13, which is' provided with sealing steam at 13a, into the inlet 14 of the reheater 16 and will continue to flow through the reheater and discharge.

by gravity from the outlet 18. The means for returning the contact material from the outlet 18 to the upper part of the reactor 10 is by means of an upright conduit v20` which extends to an elevated position within the reactor 10 and with its discharge opening substantially above the level of the contact material therein. The enlarged space within the upper part of the reactor 10 is sucient to permit the separation of the contact material from the:

Continuous coking by the contact process involves the4 uniform application of liquid hydrocarbon to the particles of the bed in such a thin film that as the bed settles or moves downward by gravity through the reactor the product vapors are continuously removed and the nonvaporized portion becomes adense, hard, dry coating. This requires a residence timeA of the bed particles within the reactor wh-ich varies from S .to 30 minutes for temperatures which are in the range of w50-850 F. ln such an Aoperation the vapors which have a virgin gas oil character, are continuously removed overhead through line 22. They may be quenched at by the application of a heavy oil recovered from a system as hereinafter described. y y

Vaporization of the lighter portions of the feed followed by the complete conversion of the remaining liquid to vapors and solid coating involves a limited heat input as the actionis both exothermieland endothermic and, therefore, substantially balanced as to heat requirements. As avresult, the contact material has onlya relatively small. temperature'- drop in its passage through the reactor. I find it desirable, however, as hereinafter described, to raise the temperatureof the discharging material to an amount somewhat higher than that required in the reaction zone and the major portion of the contact material is thus passed through the reheater 16 to be brought up to desired temperature.

The'reheater 16 is conveniently provided with a Vseries of radiant burners 26 mounted adjacent the upper or dome portion of the reactor 16 being suitably supplied with a' fuel gas through the manifold 28. By passing the contact material through a central inlet i4 a substan-tially uniform'surface 30 of flowing Contact material is exposed to the radiant heating eiects of the burner 2-6 and, as a result, `the material -is uniformly heated as it passes downwardly through the reheater. The products of combustion are conveniently removed by means of a vapor recovery channel 32 at the lower part of the reheater under control of damper 34 in the llue gas discharge line 36. Pressure control 38 maintains a uniform pressure on the system and control o-f the damper 34 at the bottom and a damper 39 at the top provides the desired degree 'of heat removal from the flue Agases which may be taken through a waste heat -boiler to the atmosphere. i

The Contact material which has been reheated then discharges at 18 into the feed leg 40 of a Y-shaped member as shown in Fig. 2, the vertical leg 41 of which `is vinterconnected with the lift leg 20. Y The bottom leg 42 is .in turn interconnected with the hydrocarbon feed line 4.6. As indicated the fresh hydrocarbon feed at e8, after passing through suitable `heat exchangers, passes through a preheater 49 and thence through an orice plate 5o and enters the liquid feed leg of the nozzle 42.

Feed vapors are prevented from passing up particle feed line 18 by introducing sealing stem or other inert vapor at 18a near the lower end of this line in sufcient quantity so that the pressure drop of the steam tlow upwards to the reheater 16 creates `a slightly higher prsure at the lower ,end of the coke feed line. Note that the coke ilow 4in this line is under-gravity packed, maximum density, conditions and that the seal steam does not lluidize the owing materials. This is a modification of the disclosure in Reissue Patent'23,237 in which I am a coinventor. In such case, a'gravity packed maximum density seal and `solids feed Vleg is used in combination with a vapor lift. In this case valve 18h replaces the feed screw 25. l

The contact of hydrocarbon with high temperature contact material immediately causes a substantial rele'a's'eiof primary llash vapors which can do all or ymost of the lifting worlt Kfor elevating the contact material through vthe lift leg conduit20 to the upper part Yof the reactor '10. 'With the substantially non-porous contact material, there is no appreciable absorption of the liquid and the liquid that .is to be converted into `dry 'colte in i reactor lit is carried on theparticles as a thin liquid film through the lift leg.l The particles in the liftrleg 2l) are thus wetted by residual liquid and evolve vapor continuously through the passage up the lift but any tendency for coke deposits or agglomeration to form will be prevented by the mass flow of the solids in the lift leg.

It is, of course, necessary to provide sutiicient vapors to do all of the lifting work and yet avoid any tendency to vaporize the feed too deeply which would not provide sufficient liquid for the reaction in the reactor. While in some cases, the amount of light stool; in the feed may be 'suiiicient or even more than enough to supply the necessary lifting vapors, very heavy stocks usually do not have enough low boiling material. In such case the lifting eff-ect is controlled by the introduction of a predetermined cut of vaporizable oit. This iS preferably obtained bv fmcticnetins the reactor overhead vapors 22 in the tower titl. such case, gas and gasoline are removed overhead at 652, a light gas oil with a 400 `to 606 F. .boiling range is removed at 64, a heavy product gas oil with an end point of from 900 to 950 F. is removed at 6.6 and recycie bottoms will be removed from lthe line 6%. Although i have shown the customary heat exchangers and reflux lines for tower 6d, only such parts Vare described as have a particular bearing yon the present invention.

The heavy product gas oil at e is usually cut at an end point from 900 to 950 F. to get maximum yields of a product having Conradson carbon content of less than 0.5%. A.t is obvious, therefore, that the primary flash vapors produced at the temperature and partial pressure prevailing in the lift leg 2? should not contain components boiling higher than the cut point of the heavy product gas oil. lf otherwise, the primary flash vapor components would recycleat a high ratio since they would be condensed at the bottom of the fractionating tower oii and revaporized in the iift leg 2i? und would thus `return with little Vor no conversion to the fractionating column.

The additional lift eifect in the leg 2t) required in order to obtain adequate solids capacity without having too much partial pressure effect with the fixed temperature required at the top of the lift leg is obtained by using a controlled portion of this heavy product gas oil at 56.' As shown `on the drawings, the 'liuc 66u is interconnected into the feed line 4S and, if necessary, some steam may be introduced through the line By appropriate control, a precise fraction of oil and steam may `be introduced into the lift leg d2 for the desired lifting effect. The bottoms 63 is usually recycled for ultimate conversion and is introduced into feed line 45E through line 68a. This bottoms may also be used as quench oil at 24.

A portion of the feed is also introduced at an upper part of the 'lift leg 2i? as byline 7d. This is of advantage in some cases to permit adding oil to obtain the maximum oil loading without difficulty from liquid accumulation in the bottom ofthe leg 2).

Control of the proportions of steam and oil are relatively simple since an excessive amount of heavy recycle in the bottom of tower 6G will indicate too much steam i and not enough oil vapors in the lift. A low initial boiling point on the recycle Vstock from the tower bottoni will conversely indicate too little steam in the lift leg. The desired liftingetiect may be maintained while adjusting the relative quantities of oil vapors and steam by simply maintaining a constant pressure drop across the orifice 50 in the lift feed line `46 since -`the orifice pressure drop and the lifting effect vary in a parallel fashion. It is, of course, understood that-'although a mol. of vaporizableoil has approximately the same partial pressure elfect as a mol. of steam, and the lifting etect of the oil is five orsix times that of the steam, its

ganarse heat 'requirement is only about three times that of steam per mol.

An advantage of this type of control of feed is that the liquid is appliedin the restricted cross section of the feed conduit (which is conveniently Y shape but may be otherwise) at the foot of 40 through which all of the contact material must pass and substantially complete uniformity is established as the contact particles pick up the maximum amount of liquid and carry it into the reactor. No xed distributing pipes extend into the hot reaction zone and there is no tendency of prematurely cokng in the distributors.

The bottom ofrreactor and the bottom of reheater 16 areso designed that equal quantities of solids are uniformly removedLfrom each unit area of the bed cross section, as by using suitable solids ow controlling devices 11 and 171thus assuring uniform particle residence time andV uniform drying of theparticles by mild' conver sion and vaporization of the lower boiling converted oils. It is also apparent that mechanical elevation is elimi-V nated with no material increase in cost of power as the vaporization of the hydrocarbons largely acts for the lifting effect. The increased pumping requirements are nominal. This leg thus acts as a conveyor, as a liquid contactor and as a partial vaporizer.

Since the required vapor velocity for lifting varies, with the square root of the particle diameter, the wide particle size variation inherent in the contact colting oper# ation may develop an excessive` velocity relative to the smallest particles. In such case, the lift leg 20 is provided with a streamlined exit target 72 which may be adjusted verticallyat 73 for the most effective opera tion.

Preferably a part of the discharge of the reactor 10 passes through a classifier 74 from which a coke product consisting of particles above in diameter may be removed through the line 76 with the remaining material returning through the line 78 back to the outlet 18 of the reheater.

The overall process that has been described has a broad application in elds where solids are to be contacted with reactants and the reaction carried to completion in a non-turbulent owing bed, but for the present only the liquid phase colting reaction will be described. The major object in coking may be to produce a maximum yield of very lightly cracked gas oil for charge to subsequent gasoline making operations, such as catalytic cracking. In this case, minimum reactor temperatures consistent with reasonable solids residence time will be employed to minimize production of gas, coker gasoline and coke. For example, a reactor temperature of 850 to 950 F. would be optimum in such cases, with control of the partial pressure effect due to lighter products and steam so as to retain all the heavier boiling feed components as a liquid to undergo the coking reaction. This would require a reactor pressure of about 20 pounds absolute and a heavy oil partial pressure of approximately 5 pounds absolute at 900 F.

It is-known from operating experience that the maximum oil loading on the equilibrium coke will correspond to about 1500-2000 barrels per day of liquid residue fromV the primary vaporization per 100 tons per hour of coke circulation. This then sets the required coke circulation for any speciiic capacity, feed stock and ultimate heavy oil recycle ratio.

Under the mild conditions chosen for this example, the coke residence time required in the reactor bed will be 20 to 30 minutes. This, together with the heat transfer requirements in the reheater, fixes the sizes of the reactor and reheater vessels and establishes the overall height of the unit Within reasonably narrow limits.

The lift leg must operate at a bottoms pressure higher than the reactor (and the reheater in the arrangement shown). This pressure diierential must be overcome by a sealing height in the reheated coke ow leg 18. With d S pounds gauge reactor pressure and 1l pounds gauge at the bottom of the lift leg, a 30 foot projected height is required for the coke feed leg for sealing. With the height and pressure diierential across the lift leg selected as above, the maximum density (pounds per cubic foot) of the ilowing vapor and solids in the lift leg is xed and may be independently controlled by means of valve 18b. The net velocity of the solids may then be selected at a value low enough to prevent undue attrition and the size of the lift leg calculated directly.

The mixture of oil vapors and steam or inert gas is then selected to give the proper partial pressure etect for the optimum extent of fresh feed vaporization. The required vapor velocity for lifting, based on the particle size and density, and the lifting vapor density is then calculated vby conventional methods. The quantity of the lifting vapor components is then determined.

The latent and sensible heat requirements for the lift leg must'be supplied by the oil preheater and the coltev heater. The maximum oil heater outlet temperature is limited by heater tube cokiug at about 850 to 900 F. for most residual stocks. The minimum heat input in the feed preheater is a matter of the relative economics of otbaining heat from the coke heater or the oil heater.

Operation is possible without any fired oil heater, if

desirable.

In the typical case above the reactor temperature would be 850 to 900 F., the oil heater outlet 750 to 850 F., coke would leave the reactor at 820 to 870 F. and the coke would be reheated to 890 to 965 F.

In other cases, it may be desirable to run the reactor at higher temperatures as for example 1000 to 1300 F. in order to produce maximum gas, gasoline, light distillate and coke from the residual oil charge. This would require coke residence time in the reactor of only 5 to l5 minutes. The coke would be reheated over` a tern` perature range of from 900 to l200 F. at the reheater inlet to ll00 to l400 F. outlet. The reactor pressure and general system pressure would have to be increased to prevent too great an extent of primary vaporization of the charge oil and retainliquid oil on the coke for conversion in the reactor bed unless heavy fuel oil was a required product. Depending on the charge stock and reactor temperature, pressure in the reactor might be of the order of 5 to 50 pounds gauge. Constant pressure control 69 is required in addition to pressure control 3S to maintain the desired conditions.

Thus it will be seen that the operating conditionswill vary over fairly wide limits, depending on theptype of charge stock and the products required but the primary conditions which are characteristic of the process will be clearfrom the above.

While I have shown and described a preferred form of embodiment of my invention, I am aware that modications may be made thereto and Itherefore desire a broad interpretation of my invention within the scope and spirit of the description herein and of the claims appended hereinafter.

I claim:

1. The method which comprises continuously supply# ing hot granular'contact material to a transfer zone to form a compact bed of. said material in said-zone, pass` ing a gaseous stream compatible with hydrocarbons into said bed under pressure to cause elevation of a portion of the contact material and/suspension in said gaseous stream, directing the gaseous stream and contact material suspended therein into a vertical elongated channel commencing below the top level of said bed, flowing the gaseous stream past the contact material in said channel to impel the contact material vertically upward in said channel, admitting into said channel liquid hydrocarbons to directly engage the upwardly moving contact material therein, said liquid hydrocarbons being admitted to a lower portion of said channel and in a'region wherein said contact materialis present in relatively high con centration as compared with higher regions of said channel, whereby said liquid hydrocarbons are completely and uniformly distributed on said contact material, the contact material in said bed and directed into said channel being at a temperature sufficiently high `to cause coking of said liquid hydrocarbons; whereby the coke produced as a result of conversion of said liquid hydrocarbons at the temperature prevailing within said transfer zoneV and in said channel is deposited substantially entirely Aonthe moving contact material.

2. The method of hydrocarbon conversion which coinprises engaging a hot granular adsorptive contact mass with a vapor stream compatible with hydrocarbons, to effect elevation of said contact mass into and through an elongated vertical channel, admitting hydrocarbons in liquid state into said channel to contact said granular mass for heat exchange 'therewith thereby eiecting at least partial vaporization of said hydrocarbons within said channel, and separating the contact mass from said vapors beyond said channel, 'said liquid hydrocarbons being introduced into said channel at a locus wherein the contact mass is in positive upward motion and is present in sufficiently high concentration to adsorb the liquid hydrocarbons contacted therewith, and the sensible heat content of said contact mass is suicient to effect vaporization of said liquid hydrocarbons and to eitect at least partial cracking of said liquid hydrocarbons to lower boiling products.

3. The method in accordance with claim 2 wherein said liquid hydrocarbons comprise hydrocarbons boiling above the range of gasoline. V

4. The method of processing a liquid hydrocarbon charge containing vaporizable hydrocarbon components boiling above the range of gasoline, which comprises continuously moving preheated discrete granular particles of non-porous coke of l/ii inch to 3% inch size through a sealed reaction zone having an enlarged space in its upper part as a compact bed moving solely by gravity, discharging the coke particles from said reaction zone into a reheating zone, passing the coke particles through said reheating Zone as a compact bed moving solely by gravity and thereby reheating the same, return-` ing the thus reheated coke particles from the reheating zone to the reaction Zone through a closed path including an upright conduit extending from below the reheat ing zoneinto the enlarged space of the reaction zone, Vpassing afhydroc'arbon feed stream under pressure into "the lower part of the upright conduit, vaporizing a portion of said hydrocarbon feed stream by contacting said stream with the reheated particles in the lower part of the upright conduit and thereby elevating the reheated colte particles as a mass upwardly through the upright conduit, applying fresh liquid hydrocarbon having a portion vaporizable at the temperature of the reheated colte particles to said 'coke particles as they move upwardly through an upper part of the upright conduit, the liquid hydrocarbon charge to coke particle ratio, the ratio ot vaporizable hydrocarbon vapors to heavier liquid hydrocarbon, and the heat supplied by the coke particles being sufficient to carry the coke particles through the upright conduit and into the enlarged space of thereaction zone bu'tinsucient to completely vaporize all the liquid hydrocarbon `applied to the coke. particles,v

converting the remaining liquid hydrocarbon on said coke particles entering into the enlarged space of the reaction zone to hydrocarbon vapors and non-agglomerating dry coke, and separately removing the last-mentioned hydrocarbon vapors from theenlarged space of the reaction zone.

5. The method of processing a liquid hydrocarbon charge as claimed in claim 4 in which the hydrocarbon feed stream passing into the lower part of the upright conduit includes a limited amount of steam to control the partial pressure in said conduit and thereby the end point and carbon residue of the primary Hash vapors.

6. The method of processing a liquid hydrocarbon charge containing vaporizable hydrocarbon components boiling above the range of gasoline, which comprises continuously moving preheated discrete granular particles of non-porous coke of 1A; inch to 3A inch size through a sealed reaction zone having an enlarged space in its upper part as a compact bed moving solely by gravity, discharging the coke particles from said reaction zone into a reheating zone, passing the coke particles through said retreating zone as a compact bed moving solely by gravity and thereby reheating the same, returning the thus reheated coke particles from the reheating zone to the reaction zone through a closed path including an upright conduit extending from below the reheat ing zone into the enlarged space of the reaction zone, passing a hydrocarbon feedY stream under pressure into the lower part of the upright conduit, Vaporizing :al portion of said hydrocarbon feed stream by contacting said stream with the reheated particles in the lower part of the upright conduit and thereby elevating the reheated coke particles upwardly through the upright conduit, applying fresh liquid hydrocarbon having a portion vaporizable at the temperature of the reheated coke particles to saidV coke particles as they move upwardly through an upper part of the upright conduit, the liquid hydrocarbon charge to coke particle ratio, the ratio of vaporizable hydrocarbon vapors to heavier liquid hydrocarbon, and the heat supplied by the coke particles being sufficient to carry the coke particles through the upright conduit and into the enlarged space of the react-ion zone i but insuicient to completely vaporize all the liquid References Cited in the lile of this :patent UNITED STATES PATENTS 2,463,623 Hutt Mar. 8, 1949 2,487,961 Angell Nov. 15, 1949 2,561,334 Bowles et al. July 24, 1951 2,587,669 Wenrich Mar. 4, 1952 2,587,670 Weinrich Mar. 4, 195.2 

4. THE METHOD OF PROCESSING A LIQUID HYDROCARBON CHARGE CONTAINING VAPORIZABLE HYDROCABRON COMPONENTS BOILING ABOVE THE RANGE OF GASOLINE, WHICH COMPRISES CONTINUOUSLY MOVING PREHEATED DISCRETE GRANULAR PARTICLES OF NON-POROUS COKE OF 1/8 INCH TO 3/4 INCH SIZE THROUGH A SEALED REACTION ZONE HAVING AN ENLARGED SPACE IN ITS UPPER PART AS A COMPACT BED MOVING SOLELY BY GRAVITY, DISCHARGING THE COKE PARTICLES FROM SAID REACTION ZONE INTO A REHEATING THE ZONE, PASSING THE COKE PARTICLES THROUGH SAID REHEATING ZONE AS A COMPACT BED MOVING SOLELY BY GRAVITY AND THEREBY REHEATING THE SAME, RETURNING THE THUS REHEATED COKE PARTICLES FROM THE REHEATING ZONE TO THE REACTION ZONE THROUGH A CLOSED PATH INCLUDING AN UPRIGHT CONDUIT EXTENDING FROM DEBLOW THE REHEATING ZONE INTO THE ENLARGED SPACE OF THE REACTION ZONE, PASSING A HYDROCARBON FEED STREAM UNDER PRESSURE INTO THE LOWER PART OF THE UPRIGHT CONDUIT, VAPORIZING A PORTION OF SAID HYDROCARBON FEED STREAM BY CONTACTING SAID STREAM WITH THE REHEATED PARTICLES IN THE LOWER PART OF THE UPRIGHT CONDUIT AND THEREBY ELEVATING THE REHEATED 